I am not sure I have the patience for a piece like this. I can tell you've put a lot of work into it. It does seem to lack that added "sparkle" of added contrast. The white and black is of course a high contrast but you loose the dramatic effect the midtone color can have since it is so close to the color of the black when stitched out. I would add a midtone light color, if you wanted to keep it monochromatic I'd use a light blue, to help with the shading of the white, and then a good medium toned blue to finish shading it like you would a pen and ink or something similar. Lovely job with your stitching though, very lovely.